1. Field of the Invention
The present invention is directed to a system and method for automated measuring of a focus portion of an exposure section of a lithography tool.
2. Background Art
Lithography systems are routinely calibrated to ensure the exposure optics are focused properly on a wafer surface. This decreases fabrication of devices that do not comply with certain tolerances by reducing printing or imaging errors caused by focus offset or focus tilt errors. One method of calibrating focus optics involves using a focus test reticle with structures that are patterned into a layer of photoresist on a wafer. The patterned structures are then evaluated manually using a microscope and recorded data is input into a spreadsheet to determine calibration compensation values. These values are used to calibrate the exposure optics. Typically, this method causes several hours of downtime a week while an operator fabricates the test wafer, analyzes if under the microscope, and enters the data. Thus, this method is time consuming, costly in terms of lost production time, and prone to errors due to reliance on human judgement. Other methods require the use of costly external equipment to generate calibration values.
Therefore, what is needed is a system and method to calibrate lithography tools by automating measurement of focus offset and focus tilt using an existing lithography system (e.g., a stepper alignment system) to evaluate a patterned structure or patterned structures.